1. Field of the Invention
This invention relates to a fuel injection control device for an internal combustion engine. More particularly, it relates to a fuel injection control device in which a piezoelectric element is employed in a fuel injection valve and in which the shape change in the element caused by application of an electric voltage thereto is utilized.
2. Related Art
It has hitherto been known to use a piezoelectric element for a fuel injection valve for controlling the fuel injection. For example, the JP Patent KOKAI Publication No. 64-69756 (1989) discloses means for stabilizing changes in capacitance of a piezoelectric element caused by changes in temperature. The piezoelectric element is increased in capacitance with the rise in temperature. If the capacitance is increased, the piezoelectric element is deformed to a larger extent for the same applied voltage because the deformation in the piezoelectric element is proportionate to the amount of the stored electric charge which is proportionate to the capacitance value. The above cited publication proposes a fuel injection control device equipped with means for detecting the change in temperature of the piezoelectric element and accordingly controlling the voltage applied to the piezoelectric element for controlling a displacement of the piezoelectric element.